Hydrogen is an important industrial gas, widely used in oil refining, and production of synthetic fuels, ammonia, and methanol. Hydrogen also is being considered for future use in hydrogen vehicles powered by hydrogen fuel cell engines or hydrogen internal combustion engines (or hybrid hydrogen vehicles, also partially powered by batteries). Most of the current supply of hydrogen is produced by steam methane reforming, using natural gas feedstock. With finite supplies of fossil-based energy resources such as natural gas and increasing prices of these energy resources, as well as the possibility of the imposition of carbon emission taxes, the cost, and eventually the availability, of hydrogen will be adversely affected unless an alternative clean and sustainable “feedstock” can be implemented.
Wind resources represent a potential source of large amounts of sustainable and clean energy. With recent increases in the cost of natural gas, the concept of using wind turbine generators in “wind farms” to supply sustainable, clean and relatively low cost electrical power to electrolysers for large scale production of “green” hydrogen is becoming an economically viable approach.
Electrolysers use DC electricity to transform reactant chemicals to desired product chemicals through electrochemical reactions, i.e., reactions that occur at electrodes that are in contact with an electrolyte. Electrolysers that can produce hydrogen include: water electrolysers, which produce hydrogen and oxygen from water and electricity; ammonia electrolysers, which produce hydrogen and nitrogen from ammonia and electricity; and, chlor-alkali electrolysers, which produce hydrogen, chlorine and caustic solution from brine and electricity.
Water electrolysers are the most common type of electrolyser used to produce gaseous hydrogen. Oxygen also is an important industrial gas, and the oxygen generated may be a saleable product. The most common type of commercial water electrolyser currently is the alkaline water electrolyser. Other types of water electrolysers include PEM water electrolysers, currently limited to relatively small production capacities, and solid oxide water electrolysers, which have not been commercialized. Alkaline water electrolysers utilize an alkaline electrolyte in contact with appropriately catalyzed electrodes. Hydrogen is produced at the surfaces of the cathodes (negative electrodes), and oxygen is produced at the surfaces of the anodes (positive electrodes) upon passage of current between the electrodes. The rates of production of hydrogen and oxygen are proportional to the DC current flow in the absence of parasitic reactions and stray currents, and for a given physical size of electrolyser.
Wind farms consist of a number of wind turbine generators, generally spread over a significant geographical area. Wind farms typically generate AC electricity for delivery to an AC utility grid, although generation of DC power also is possible. AC electricity can easily be transformed to higher voltages for efficient transmission of high power over long distances. Wind farm total output can range from tens of MW to hundreds of MW. The electrolyser module size could range from below 1 MW up to 5 MW. Dedicated hydrogen generation using electrolyser modules as loads connected to a large wind farm will therefore employ a significant number of electrolyser modules.
Large scale, low cost production of “wind hydrogen” (hydrogen produced by water electrolysis using wind power) requires capture of a high percentage of the wind power generated, the output of which is variable over time. This requirement necessitates firstly the use of multiple large scale, low cost water electrolyser modules that can act as highly variable loads to cover a wide range of operating power, from low to very high power densities. An appropriate water electrolyser module design is disclosed in the co-pending application which is incorporated by reference herein in its entirety. Other necessary elements are an efficient, low cost, and flexible electrical power dispatch system and operating method to distribute the wind power to the multiple water electrolyser modules, as well as effective control of the electrolyser modules to ensure load matching to the wind farm output. An appropriate electrical power dispatch system and operating and control methods are described herein. Although the description of the invention herein relates to “wind hydrogen”, it is to be understood that the invention also is applicable to electrolytic production of other chemicals, for example, direct production of “wind ammonia” using the electrolyser described in US 2008/0193360.